Conventionally, among various types of suspension devices for suspension of an axle from a frame, a suspension device with a plurality of layered leaf springs, which is simple in structure, less expensive and highly strong and durable, has been extensively used for a truck or other vehicle.
In such suspension device, it is a matter of course to mount the plural layered leaf springs so as to enable positioning of the axle even if any of the springs breaks, which however disadvantageously results in increases in weight of the vehicle. Thus, a suspension device has been studied which comprises a single leaf spring for weight saving.
There exists, for example, the following Patent Literature 1 as prior art document relating to this kind of leaf suspension.